Optical disks for storing information, e.g., in binary form, are provided with a plurality of optical xe2x80x9cfeaturesxe2x80x9d, i.e., marks and/or shapes which can be optically detected and used, e.g. for read and/or write operations. Features may represent content information, such as information which can be ultimately provided to the user (regardless of whether the user is a human, a computer or other device), but may also include other information such as information used for purposes such as focus or tracking (or other servo functions), sector navigation or addressing (or other access operations), testing purposes, data security purposes, quality control purposes and any of a number of other purposes, as will be understood by those of skill in the art after understanding the present disclosure.
Disks with features thereon can be formed using any of a number of processes. One operable process falls generally in the category of injection molding. In injection molding (of any of a number of objects, including optical disks), a mold cavity having a size and shape corresponding to (e.g. after thermal shrinking) the size and shape of a final object, is injected with heated (fluid) thermoplastic material. After cooling e.g. to the glass transition temperature, the mold is opened and the object is removed.
In some situations, features on an optical disk may represent binary digits (bits), or groups of bits. In most situations, features can be considered to be either in the form of a protrusion or in the form of a depression. The difference can be most readily described in the context of a xe2x80x9cstamperxe2x80x9d (i.e. a device used in a molding device for forming a disk, the stamper having a generally planar surface and a plurality of protrusions extending from the planar surface into the mold cavity or depressions receding from the planar surface away from the mold cavity. Protrusions on a stamper provide depressions in the molded disk and depressions in the stamper provide protrusions in the molded disk. Features can be formed on one surface of the disk, or on both surfaces (in which case, two opposed stampers are used in the molding device. Although descriptions of a stamper-formed disk are believed useful in describing the difference between protrusion disk features and depression disk features, the present inventions, described below, is not limited to use in disks which are molded, but can be used in disks where features are formed in other fashions (such as by ablation, injection-compression, etching, or other methods).
In typical applications, bits or bit groups are represented by bumps (small protrusions) or pits, (small depressions). Typically, such bumps or pits are positioned along one or more spiral or circular tracks on at least one surface or layer of the disk. Disks may also contain features which do not directly represent data bits. For example, there may be features such as grooves or lands, typically in an extended circular or spiral pattern, e.g. for defining one or more tracks. In some cases, the tracks may have small-scale periodic or other deviations from a circular or spiral pattern (e.g. xe2x80x9cwobbledxe2x80x9d grooves), such as for tracking and/or timing purposes.
When optical read/write devices include some type of detection of reflectivity (or some other parameter related to reflectivity) as the read/write beam is successively in alignment with lands, bumps, pits, grooves, and the like, typically, reflectivity changes detectably as the beam crosses a leading or trailing edge of a feature. Accordingly, if, e.g., a read/write beam is maintained aligned with a track which bears pits or bumps, a reflectivity transition will ideally be detected near the (track-wise) leading edge and trailing edge of each bump or pit along the track and accordingly, the difference in timing between leading edge and trailing edge transitions in reflectivity are indicative of the (track-wise) length of the bump or pit. In this way, the presence and/or length of a bump or pit can be detected and converted to bits or bit patterns (according to any of a number of encoding schemes).
A number of aspects of the size, shape, distribution or arrangement of features on the disk (and/or of electrical, optical or other parameters associated with their detection) are of significance in the read/write operations. Among these are the as-detected track-wise or radial size of the features, the z-dimension size of the features, the radial spacing of features, the track-wise spacing of features and/or the DC offset of detection signals, particularly for high frequency (short-length) marks compared to relatively longer marks. The design of encoding schemes and design of the read/write device (including size and shape of the medium, wavelength of the read/write beam and other factors) place constraints on the size and/or shape of features which are desired and/or operable in an optical disk data storage system.
Many previous disk configurations provide a relatively thick, substantially transparent, plastic or other substrate through which the read/write beam passes, before reaching a data layer (i.e., a layer which has readable or writeable features formed or formable thereon). As used herein, xe2x80x9cread/writexe2x80x9d refers to beams, devices or processes which involve only reading, only writing, or both. In previous typical optical disk configurations, the effective thickness of such substrate (or other relatively thick covering layer) was sufficiently large that the surface of the interface which does not contact the data layer (e.g. the air-substrate interface) was substantially outside the depth-of-field of the optical system used to read or write data, and accordingly, at least some important optical parameters were substantially unaffected (within tolerances required for successful operation of read/write operations) by the presence of the layer (i.e., by the requirement that the read/write beam traverse the substrate before reaching the data layer).
However, it is believed certain limitations on performance arise from the provision of a relatively thick substrate or similar layer. Accordingly, it would be useful to provide a system, method and apparatus which can achieve desired as-detected feature sizes and/or shapes without being limited to relatively thick substrates (or other layers through which the read/write beam must pass before reaching the data layer) for the read/write medium.
The present invention includes a recognition of the existence, nature and/or source of certain problems, including as described herein.
According to one aspect of the present invention, it is recognized that, in at least some situations, providing a relatively thin film over some or all of an optical disk data layer can affect items such as the xe2x80x9cas-detectedxe2x80x9d size or shape of bumps or pits or other features (e.g., compared to the actual physical size of the feature, e.g. as molded) and that, accordingly, it can be advantageous to correct for and/or account for such effects. As used herein, xe2x80x9cas-detectedxe2x80x9d size, spacing or magnitude refers to whatever feature size, spacing or magnitude is detected by (or indicated by or derivable from electrical or digital signals indicative of beam reflectivity or other feature-indicative parameters) an optical disk read/write device (e.g. based on time difference between a beam crossing a leading feature edge and a trailing feature edge, including as described below). In one embodiment, the effect of a thin film is corrected-for by forming features which have an actual, physical, size different from the desired as-detected feature size, e.g., so that after providing the thin film, the as-detected size of the feature (including effects caused by the presence or thickness of the film) is equal to the desired as-detected feature size. The desired as-detected feature size may be the size for any of a number of different features (including bumps, pits, grooves, lands and the like), may be sizes or shapes in any of a number of different dimensions or spacings (including, e.g., track-wise length, radial width, z-dimension magnitude, track-wise distribution, inter-track distances or distributions and the like), and desired as-detected dimensions may be selected to achieve any of the number of different goals (such as providing a minimum, predetermined or type-averaged DC offset, achieving desired mark/space ratio, reducing asymmetry, increasing resolution, decreasing jitter, decreasing cross-talk, increasing signal to noise ratio, and the like, and/or combinations thereof).
Although features of the present invention are believed useful in a number of optical storage contexts, the present invention is believed to be especially useful in the context of a first surface medium, including as described in U.S. patent application Ser. Nos. 09/560,781 and/or 09/315,398, incorporated herein by reference. In the preferred embodiment, the optical medium is a first-surface medium. Although it may be subject to more than one definition, in one embodiment, the first-surface optical medium refers to a medium in which the read beam during a read operation is incident on or impinges on information content portions of the first-surface optical medium before it impinges on a substrate of the first-surface optical medium. The xe2x80x9cinformation content portionsxe2x80x9d can be defined as portions of the optical medium that store or contain servo data, address data, clock data, user data, system data, as well as any other information that is provided on the optical medium. The xe2x80x9cinformation content portionsxe2x80x9d can be integral with the substrate such as the case of a read-only medium. The information content portions can also be separately provided. In such a case, the information content portions can be, for example, an information layer of a writeable medium.
In one additional or alternative definition, the first-surface optical medium can refer to an optical medium having a tangible thickness in which a read light beam during a read operation traverses less than 100 micrometers of this thickness before impinging on the information content portions.
In at least some approaches, a first surface medium may be formed by a process which includes molding in a molder device 1812 (FIG. 18) such as an injection-molding device, to form a pre-disk having features formed on at least a portion of a surface, (including by a process generally as described in U.S. application Ser. No. 09/652,975, filed Aug. 31, 2000, optionally providing a metallic or other reflective material, and forming a thin film using a coater 1814 (e.g. by a sputtering process, electron beam process, spin coating, an ion deposition process, electro-deposition process or the like) substantially over the data layer or surface. Those of skill in the art, at least after understanding the present disclosure, will understand appropriate injection molding or other pre-form forming apparatus and will understand appropriate sputtering apparatus or other apparatus for coating with one or more thin films. The film is preferably sufficiently think that a substantially first-surface medium is the result. Typically, such a thin film will be less than about 200 nanometers thick (i.e., in the z-dimension), more preferably less than about 130 nanometers thick and even more preferably less than about 100 nanometers thick. In one embodiment, the film serves the function of at least partially enhancing contrast or bit-detectability. However, many type of thin films can be provided including protective films, anti-reflective films and the like. In one embodiment a dielectric film, formed substantially of SiOxNy (silicon oxynitride) is provided.
As noted above, in typical previous devices where the read/write beam travels through a relatively thick substrate (such as about 100 micrometers or more) before reaching a data layer, the presence or thickness of the relatively thick substrate was considered to have little effect on certain parameters such as as-detected feature sizes, DC offset, signal to noise ratio and the like. However, it has been found that thin films can have an effect on the as-detected feature size, signal to noise ratio and/or DC offset and the like, which can be significant for at least some optical storage systems (i.e. can affect efficiency, reliability and similar aspects of the system), especially for first surface media. Accordingly, in one aspect of the invention, the physical size or shape of features, or their spacing or arrangement on a data layer is adjusted to compensate for, or take into account, the effect of a thin film. In one embodiment, e.g., when a feature involves a pit or depression, with respect to the land region, a track-wise (longitudinal) dimension of the feature is increased, preferably by an amount about equal to twice the projection of a feature side wall film thickness on the data plane. In another embodiment, particularly useful for features which project outwardly or upwardly (i.e., in the z-dimension) with respect to the data surface, the physical feature size is made smaller than the desired as-detected size, so as to at least partially account for the presence of and/or thickness of, the thin film, such as being decreased by an amount equal to about twice the projection of the feature sidewall film thickness on the data plane.
In some approaches, adjustment, for compensating for or accounting for the effects of a thin film, can be achieved empirically, such as by adjusting feature sizes and testing the results, in an iterative fashion until desired results (or ranges of results) are achieved (such as desired data discrimination, desired signal to noise ratio and/or desired DC offset is obtained).